BOULDER LITHOLOGY SURVEY, TIBES CIVIC-CEREMONIAL SITE, PUERTO RICO

Tibes archaeological park, located just north of Ponce, Puerto Rico, is the site of nine bateys (ball courts) and plazas, and is thought to have served as a gathering and ceremonial center of the Taino. The Pre-Columbian stone structures are composed of rounded boulders of various lithologies. Representative rock types and source areas had not been established previously, although the Portugues River bed adjacent to the site would have been a convenient material source.

Our detailed tape and compass survey recorded locations, lithologies, and intermediate dimensions of the boulders in each structure. More than 5500 boulders were censused overall, ranging in size from as little as 10 cm to upwards of 80 cm. Transects of the river bed were also surveyed to compare percentage lithologies of point-counted boulders (n=663) to those in the structures. The same dominant lithologies are found in river bed and structures, mostly in similar proportions: tuffaceous lithic sandstone 19.8% (river) vs. 17.8% (structures), volcanic breccia 8.4% vs. 16.7%, quartz diorite 11.0% vs. 12.9%, green tuff 17.9% vs. 12.5%, gabbro 8.4% vs. 8.9%, brown tuff 5.1% vs 9.1%, gray tuff 11.6% vs. 7.5%, andesite porphyry 4.5% vs. 6.0%. Rarer lithologies (5% or less, each) found in both river and structures include other tuffs, limestones, and breccias.

One rock type, a calcareous sandstone, makes up approximately 1% of boulders in the structures but is entirely absent from the river bed. The sandstone slabs, ranging from 12 to 41 cm intermediate dimension, show no signs of rounding by river transport, and display the majority of the rare petroglyphs found in the park. A source area for this sandstone could be less than a kilometer from the site, outside the river drainage basin. We are continuing to examine the spatial variation of other boulder lithologies and sizes among the various ball courts and plazas, to investigate any selective use of available materials in their construction.